This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-138881, filed May 19, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to a supervisory control system for municipal infrastructures, for example, supervisory control of widely distributive processes for, for example, water, gas, and power supplies and environment measurements, and in particular, to a decentralized supervisory control system comprising one or more supervisory devices interconnected with one or more distributed control devices.
In conventional wide-area supervisory control systems, supervisory control is provided by concentrating information from distributed controllers and sensors at a supervisory device installed in a central supervisory room. Thus, a network-based decentralized supervisory control system must be applied so as to easily collect requests for load distributions and sensor information scattered over a wide area and to use various communication means to distribute the data to the center.
An example of a conventional decentralized supervisory control system is shown in FIG. 1. As shown in this figure, the decentralized supervisory control system comprises, for example, a plurality of distributed control devices 3 each connecting to a controller 1 for valves in water lines and to a sensor 2, generally one supervisory device 4, and a communication path 5 connecting the distributed control devices 3 and the supervisory devices 4.
The distributed control device 3 receives PIO data and sensor information from the controller 1 and the sensor 2, respectively, and sends out these data to the supervisory device 4 via the communication path 5. The supervisory device 4 comprises an antenna 4 for receiving time signals, a display 4b, a time setter (TS) 4c, a database (DB) 4d, and a image processor (IP) so that the timer setter (TS) 4c can add to data from each distributed control device 3 the time at which the data was obtained (a time stamp) and so that the database (DB) 4d and the image processor (IP) 4e can process the data into images in a predetermined form for display on the display 4b. 
FIG. 2 shows an example of how the distributed control device 3 is installed in a decentralized supervisory control system applied to a water line plant.
A water line 11 buried under a roadway 10 has valve 12, a controller 1 including an actuator or controlling opening and closing of the valve 12, and a sensor 2 for measuring flow rate and pressure. The valve 12, the controller 1, and the sensor 2 are placed in a 13 that is occluded by a cover 14. In addition, a sidewalk 15 at a side of the roadway 10 has a road station enclosure 16 installed thereon and having the distributed control device 3 installed therein. The road station enclosure 16 and the manhole 13 are connected together through a wiring duct 17, with signal wiring 18 and power supply wiring 19 accommodated in the wiring duct 17 to electrically connect the distributed control device 3 to the controller 1 and sensor 2. Additionally, the distributed control device 3 has communication wiring 20 drawn therein and connected to the communication path 5 and also has power supply wiring 21 drawn therein.
On the other hand, a data structure used by the supervisory device 4 will be explained with reference to FIG. 3. The time at which such data was obtained (a time stamp) is conventionally added to the data as an attribute of the process data. Illustrated data 212 includes one data 212e and time data 212a to 212d accompanying the data 212e. The time data comprises data 212a indicating year, month, and day, data 212b indicating hour, minute, and second, data 212c indicating millisecond, microsecond, and nanosecond, and data 212d indicating a data type.
In this manner, the data structure has detailed data such as year, month, day, hour, minute, second, millisecond, and microsecond added to the one data. The detailed time stamp data are effective in determining the order of individual data, but they are excessively detailed as man-machine supervisory data. Furthermore, when the local distributed control device carries out a transmission to the central supervisory device via the communication path, that is, when 32-bit data is transmitted, a triple amount of data, that is, 32xc3x973-bit time data is added before the transmission, thereby increasing transmission loads.
In addition, since the distributed control device generally has its own supervisory section, this supervisory section is often managed and maintained online. In this case, an exclusive maintenance terminal is connected to the device to make adjustments such as changes in the organization of screens and Io settings. Since, however, a supervisory control section, a date distribution section, and the like are operating continuously, screens or data may be distributed to the central supervisory device before screen updating or independent debugging is completed, resulting in transmission of incorrect data.
Additionally, if a public line is used as the communication path, it is important in terms of security to provide means for preventing incorrect telephone numbers, intended leakage of supervisory data, and invalid accesses.
It is an object of the present invention to provide a decentralized supervisory control system that can prevent errors such as transmission of incorrect data between a distributed control device and a supervisory device even if a screen is changed for supervision.
To attain this object, according to the present invention, a distributed control device connected to a central supervisory device via communication path comprises an I/O interface for transmitting control signals to a controller for a controlled device and obtaining inputs from a sensor, data storage means for storing PIO data from the controller, sensor information, and additional information such as data obtention time, time obtention means for adding a time to the data when the data is stored in the data storage means, data distribution means for distributing the PIO data, the sensor information, and other supervisory information, supervisory control means for carrying out supervisory control using the PIO data from the controller as well as the sensor information, a network interface for communicating with other distributed control devices and the supervisory device, and communication means for connecting the distributed control device to the other distributed control devices and supervisory device. The distributed control device is also characterized by comprising means for inputting information for use in supervising a plant, means for accumulating the information, means for sending out the information from the information accumulation means to the supervisory device via the communication path, means for processing the input or the accumulated information into information that is sensed by an operator and presenting this information to the supervisory device via the communication path, means for controlling the plant in accordance with the operator""s commands obtained from the supervisory device via the communication path, and means for outputting signals to the plant in response to the operator""s commands, wherein:
the supervisory device comprises means for converting the information obtained from the distributed control device via the communication path and used to supervise and control the plant, into information that is sensed by the operator, and presenting the converted information to the operator, and means for replacing the operator""s commands with signals and communicating the replaced signals to the supervisory device via the communication path.
With these means, each distributed control device adds a time stamp to the PIO data and sensor information, processes the obtained data into the information that is sensed by the operator, and sends this information to the supervisory device, which simply displays the processed data. Therefore, data to be supervised by the operator is created by the distributed control device instead of the supervisory device, preventing errors in transmissions of the supervised data as caused by other processing such as changes in a screen.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.